The Kzinti in the Trek Universe
The Kzinti homeworld is called Kzin and it orbits 61 Ursae Majoris about 31 light-years away. Humans of the late 21st century, pre-warp Earth headed to towards this system in the great migrations from Earth. On their way, they encountered the Kzinti and the first of three wars between the two races began. The Kzinti are violent, expansionistic, and convinced of their own superiority. The Kzinti lost each time to Earth's forces (then mostly sub-light ships) and they never got over that they lost to an "omnivorous" race.
The stellar cartographers of Starfleet named the Kzinti area of space the Kzinti Hegemony. Their own name for their government can be translated as The Patriarchy.
By 2151 Starfleet had pushed the Kzinti back to their homeworld and Archer IV, also orbiting 61 Ursae Majoris, was established as an Earth colony. By 2371 it was a fully inhabited Federation planet. The confusion came about because the Kzinti call any world they inhabit as their "homeworld". The Federation not only defeated the Kzinti, they humiliated them.
So we have a chauvinistic race, that has a government called the Patriarchy, who is convinced they are superior to all other races and yet still got their asses kicked by the Federation. If you think I am not going to have a go at that then you have not been here reading this blog for long!
Besides. Star Trek was doing Social Justice in the 60s. This is a perfect subject to do in a Star Trek RPG.
I am planning on making them my "little bads" or at least make them appear to be the big bads. They are not, they are just a pain in the ass. Their area of space is close (ish) to other parts of the federation including Memory Alpha. This works out well since the first mission of the USS Protector is a "milk run" to Memory Alpha. Yes I am making the first adventure a run to the Federation "Library" as an homage to all the library runs I made to read books about space, astronomy and then Lovecraft and Star Trek.
A couple reasons that make the Kzinti great for my BlackStar game is they are superstitious, still believe in magic and ghosts (and why not, they have a high level of psionic individuals in their population) and maybe best of all they allow me to use some ideas I have created for other games that would find fertile ground here.
Rebuilding the Kzinti for BlackStar
I am setting my BlackStar game between the TOS and TNG eras. A time, calendar wise that also corresponds to the time when I first discovered the Kzinti and a time of evolution of Trek and in particular the Klingons.
In a fairly real sense, the Kzinti represent stepping stone really between the "old" and the "new" Klingons. The honor, the violence, and even the warrior caste system of the Kzinti can be added to the old, or TOS Klingons to create the newer TNG and movie era Klingons.
Since this "in-between" time is also covered fairly well by the FASA Trek game I will turn to it for ideas.
FASA Trek, much like Starfleet Battles, can be seen as an alternate evolution of the same core Trek from the Original Series on. I am already borrowing a lot from FASA Trek, so I might take some of their ideas on Klingons and use them for the Kzinti.
In particular, their philosophy of "That which is not growing is dead." to explain their desire to expand their territory again.
I am not going to make Kzinti available as a playable race. If I want something like that I'll go with Caitians like M'Ress and Srrel.
Kzinti WarriorKZINTI WARRIOR
ARMOR CLASS: 7 
HIT DICE: 2
SAVING THROW: 17
TOTAL HIT BONUS: +2
MOVEMENT: 12 (12 when climbing)
SPECIAL: Dark vision 90 ft, Climb
ATTACK: Claws (1d6) or by weapon
ARMOR CLASS: 9 
HIT DICE: 1-1
SAVING THROW: 17
TOTAL HIT BONUS: +1
MOVEMENT: 9 (0 when climbing)
SPECIAL: Dark vision 90 ft, Climb, Psychic Blast,
ATTACK: Psychic Blast (1d6)
Starships & Spacemen
Kzinti PsychicKZINTI WARRIOR
Encountered: 2d4 (2d10)
Movement: 120' (40')
Psionic Potential: inactive
Armor: 7 (2 with power armor)
Combat Skill: 12
Damage: By weapon
Encountered: 1 (1d6)
Movement: 90' (30')
Psionic Potential: active
Armor: 9 (5 with power armor)
Combat Skill: 6
Attacks: 1, Psychic Blast
Kzinti Warriors are 2.1-meter tall 220 kg, barrel-chested felinoids. They can attack with claws but prefer weapons. They have long tails and hairless ears. Their eyesight is good in the dark, but their sense of smell is superior to that of Terrans. They are voracious carnivores and must consume raw meat. They can survive on replicated food, but they will claim it has "no life" to it.
They are a superstitious race and will not use the weapon of a fallen foe believing that the ghost of that foe still haunts the weapon.
Kzinti Warriors will often add honorifics to their name and title. So a captain of a Kzinti warship that has never been defeated might call himself Vrust-Captain, the Undefeated.
Kzinti Psychics almost apper to be a different race. They are much smaller, 1.8-meter, and much thinner at 130 kg. They are hunched over and appear to ready to fall over. They are powerful psychics and know many attack and defense modes. They are often used to extract knowledge and secrets from other species. Even though they appear frail they are driven by the same desires that affect the warrior caste. This has caused many among the psychic class to adopt cruelty to others weaker than themselves which is even marked by Kzinti standards.